Anchors are used for anchoring a downhole tool in the direction traverse to the longitudinal direction of the tool for resisting the torsional forces that the tool is subjected to during e.g. drilling.
A known solution is disclosed in U.S. Pat. No. 5,070,941, in which anchors anchor a tool by use of hydraulic. The anchors are placed in a recess in the circumference of the tool so as to be out of the way of the central elements of the tool placed in the centre of the tool. When anchoring the tool, the anchors are moved outwards, most of the anchor thus projecting from the side of the tool.
Since most of the anchor projects from the tool, the anchor will become somewhat tilted when exposed to the longitudinal force created when the tool is in use. In this way, each anchor is forced to be inclined in the recess in the tool and outwards towards the surrounding casing or the like. It is often seen that anchors get stuck in this inclined position, and therefore cannot be retracted into the tool again, when the anchors are forced to be tilted in the tool. As a result, the whole tool is stuck downhole.
Furthermore, in order to mount the anchor in a recess in the tool, the edge of the recess needs to be chamfered. When the anchor is mounted in the recess, the chamfering leaves a little slot in which dirt may be gathered. In addition, when the anchor is used for anchoring the tool and subsequently is retracted into the tool again, dirt in the well fluid is retracted into the little slot and further into the recess. In this way, the dirt may be the decisive factor for the anchor to get stuck.